International audienc

In seismic reliability analysis the total failure probability is determined by combining the fragility curverepresenting the response of the structure to seismic excitation -with the seismic hazard curve. The determination of fragility curves has a long tradition in the nuclear industry and reaches back to the 1970s. Since the late 1990s also for ordinary buildings seismic reliability analysis became more important and formed the bases for the development of new seismic standards. Several methods are available to build fragility curves relying on different assumptions and restrictions, level of detail and type of failure modes under consideration. In this paper, different fragility analysis methods are described and their advantages and disadvantages are discussed: (i) the safety factor method, in which the fragility curve is estimated on an existing deterministic quasi-static design; the numerical simulation method, in which the parameters of the fragility curve are obtained by (ii) regression analysis or (iii) maximum likelihood estimation from a set of nonlinear time history analysis at different seismic levels; (iv) the incremental dynamic analysis which is based on numerical simulation and the scaling of accelerograms until failure. These four fragility analysis methods are applied to determine fragility curves for the 3-storey reinforced concrete shear wall building of the SMART2013 benchmark project. Advantages and disadvantages of the methods are illustrated and the impact of the simplifying assumptions (e.g. lognormal curves, scaling) are accessed.

The paper reports the main findings of a series of shaking table tests on a 3-story 1/4-scale reinforced concrete model characterized by strong asymmetry, representative of a nuclear building. The specimen was subjected to 13 bi-directional input ground motions with increasing maximum acceleration from 0.05 to 1.0. g, which induced significant torsion and a nonlinear response. The tests were conducted on the AZALEE shaking table (Saclay, France) as part of a wide research program launched by the French Atomic Energy and Sustainable Energies Commission (CEA), Electricité De France (EDF) and the International Atomic Energy Agency (IAEA), titled, "Seismic design and best-estimate Methods Assessment for Reinforced concrete buildings subjected to Torsion and nonlinear effect (SMART)." Based on the analysis of the test results, the following conclusions were drawn: (a) moderate damage occurred on the specimen (mainly close to the geometric singularities) as revealed by the crack patterns observed at the end of the seismic test sequence; (b) the model responded mainly in the torsional mode; (c) an important specimen stiffness reduction was observed with a shift of the first peak frequency almost equal to 50%; (d) the seismic margins assessment carried out with two distinct failure criteria (frequency shift and inter-story drift) showed an important specimen robustness for high seismic amplitude as well

This paper reports the main results and conclusions of an International Benchmark jointly organized within the framework of a wide research program launched by the French Atomic Energy and Sustainable Energies Commission (CEA), Electricité De France (EDF) entitled "Seismic design and best-estimate Methods Assessment for Reinforced concrete buildings subjected to Torsion and nonlinear effect (SMART)". This research program included first an experimental campaign on reduced scaled specimen and shaking table tests, and second, a Benchmark exercise based on the contest of numerical methods and methodologies referring to the experimental results from the tests. The objectives of the Benchmark exercise were to compare the results obtained by conventional seismic assessment methods with those obtained by best-estimate methods, to compare the methodologies of taking into account uncertainties in the numerical analyses when a probabilistic assessment should be performed and to create an event allowing the international community in earthquake engineering to discuss the aforementioned topics of common interest. According to the analysis of the results, it turned out that (a) conventional methods are clearly able to provide relevant seismic assessment at the design level; (b) when dealing with overdesign seismic loadings, advanced best-estimate methods seem to be able to capture several key indicators such as the frequency shift of the peak of the response spectra; and (c) the blind nonlinear computations demonstrate a high robustness level of the specimen based on both structural and local damage indicators (frequency shift and inter-story drift, respectively)

In this paper, the main findings and conclusions drawn from the second international benchmark named SMART 2013 and jointly organized by the French Sustainable Energies and Atomic Energy Commission (CEA) and Electricité De France (EDF) within the framework of a wide research program entitled "Seismic design and bestestimate Methods Assessment for Reinforced concrete buildings subjected to Torsion and nonlinear effects" (SMART) are presented. A 1:4-scaled reinforced concrete (RC) specimen, representing a part of a nuclear auxiliary building and designed according to French guidelines for a PGA level equal to 0.2 g, was subjected to shaking table tests; results of this experimental campaign are used as reference data for this benchmark. The input ground motions considered in the seismic loading sequence are mainly natural bi-axial signals (main shock and aftershock) recorded during the Northridge earthquake that took place in California, USA in 1994 and have a PGA (Peak Ground Acceleration) about 1.8 g. These high-intensity seismic loadings allow assessing the relevancy of nonlinear numerical models when they have to deal with strong nonlinearities due to concrete cracking. The results produced by the 42 teams which participated in the international benchmark show that (i) the dynamic behavior of the specimen is well captured when dealing with the design level, (ii) the displacement are underestimated when dealing with the beyond design behavior, (iii) the peak frequency shifts are well captured and (iv) the damaging effect of the Northridge aftershock is almost null. Last, seismic safety margins of the specimen are quantified by two mechanical indicators; the results confirm the fact that the RC specimen which was designed according to the codes applicable in the French nuclear industry, exhibits noticeable good performance level regarding collapse prevention.